The present invention relates generally to the detection of cancer and precancerous conditions and more particularly to the detection of cancerous and precancerous cells in cell smears.
Because a sufficiently effective method has not yet been developed to prevent cancer, cancer research has focused on the most effective ways to treat cancer. As different as the various forms of treatment have been--ranging from excision to radiation to chemotherapy--all treatments have relied upon one crucial step, the detection of cancer. The importance of detection cannot be stressed enough. Early detection not only indicates the presence of cancer (or of a precancerous condition) but also may give an indication as to where the cancer originated and what type of treatment will be the most safe and effective. In addition to being used to detect cancer early, detection methods may also be used to determine whether treatment methods have been successful in eradicating cancer from a patient.
At present, methods for detecting most forms of cancer have relied primarily on the use of X-rays, nuclear magnetic resonance, nuclear radiation or invasive methods based on chemical laboratory analysis and biopsy. To detect cervical cancer, one commonly employs the Pap smear technique. Pap smears are typically performed by obtaining a sample of cells from a patient and smearing them on a slide. Typically, the cells are stained to make them more visible under microscopic examination. The smeared slide is then examined under a microscope, typically by a physician or trained technician. The physician or technician detects cancerous or precancerous cells in the smear based on certain criteria, such as cell morphology. As can readily be appreciated, this means of detection is not exact and often results in errant results. Moreover, this technique is cumbersome and time consuming and is not in situ or in real time.
Recently, optical spectroscopy has been investigated as a means of detecting cancer. For example, in U.S. Pat. No. 5,042,494, inventor Alfano, which issued Aug. 27, 1991, and which is incorporated herein by reference, there is disclosed a method and apparatus for detecting the presence of cancerous tissue using native visible luminescence. The tissue to be examined is excited with a beam of light that causes the tissue to fluoresce over a spectrum of wavelengths. The intensity at which the the excited tissue fluoresces can be measured either over a spectrum or at a predetermined number of preselected wavelengths. By determining the wavelength(s) at which maximum intensity(ies) are attained for the tissue in question and by comparing these peak wavelengths, either visually or electronically, to the peak wavelength(s) derived from a known non-cancerous tissue, or by comparing the luminescence spectrum of the excited tissue with the luminescence spectrum of a known non-cancerous tissue and/or known cancerous tissue or the excitation spectra of the excited tissue with the excitation spectra of known cancerous and/or known non-cancerous tissue, one can determine the carcinomatoid status of the tissue in question.
In U.S. Pat. No. 5,131,398, inventors Alfano et al., which issued Jul. 21, 1992, and which is incorporated herein by reference, there is disclosed a method and apparatus for distinguishing cancerous tumors and tissue from benign tumors and tissue or normal tissue using native fluorescence. The tissue to be examined is excited with a beam of monochromatic light at 300 nm. The intensity of the native fluorescence emitted from the tissue is measured at 340 nm and at 440 nm. The ratio of the two intensities is then calculated and used as a basis for determining if the tissue is cancerous as opposed to benign or normal.
In U.S. Pat. No. 5,413,108, inventor Alfano, which issued May 9, 1995, and which is incorporated herein by reference, there is disclosed a method and apparatus for examining a two-dimensional region of a tissue sample. This is accomplished, according to one embodiment, by illuminating, i.e., exciting, the two-dimensional tissue sample with light at a first wavelength. The resultant fluorescence is then measured at an emission wavelength as a function of location within the two-dimensional tissue sample. The two-dimensional tissue sample is then illuminated again with light at a second wavelength, and the resultant fluorescence is measured at the same emission wavelength. The two excitation wavelengths and the emission wavelength are appropriately chosen so that the ratio or difference of fluorescence intensities at the emission wavelength is indicative of the carcinomatoid condition of the tissue. A value, such as a ratio or difference, of the respective intensity measurements obtained at each location of the tissue sample is then calculated. These values are then compared to appropriate standards, and the results are depicted in the form of a map. The invention is premised on the discovery that certain native, commonly-occurring molecules, such as collagen, NAD+/NADH, NADP+/NADPH, flavins, tryptophan and elastin fluoresce differently in cancerous tissue than in non-cancerous tissue.
It should be noted that, in the three patents discussed above, the sample examined is a tissue, not a cell smear.
In U.S. Pat. No. 5,635,402, inventors Alfano et al., which issued Jun. 3, 1997, and which is incorporated herein by reference, there is disclosed a technique for determining whether a cell is malignant as opposed to non-malignant using extrinsic fluorescence spectroscopy. The technique is premised on the principle that certain fluorescent dyes preferentially stain malignant cells as opposed to non-malignant cells. Accordingly, by exposing a cell to the fluorescent dye, irradiating the cell with light of such a wavelength as to cause the dye to fluoresce, measuring the intensity of fluorescence at a wavelength indicative of fluorescence of the dye, and comparing the fluorescence intensity to standards obtained from malignant cells and nonmalignant cells, it is possible for one to accurately classify the cell as being either malignant or non-malignant. The present invention also relates to an automated system which applies the principles of the aforementioned technique to depict the spatial distribution of cells within an area of a Pap smear-type sample and to characterize each of the cells as being malignant or nonmalignant.
It is to be noted that, in the case of the aforementioned patent, extrinsic fluorescence spectroscopy, as opposed to native fluorescence spectroscopy, is used.